Electronic devices such as server apparatuses employ a structure including a plurality of printed board units to enhance mounting efficiency of circuit devices and electronic components in a housing and to enhance cooling efficiency of apparatuses.
Concerning an apparatus structure including a printed board in a housing, Japanese Laid-Open Patent Publication No. 09-08480 discloses mounting a printed wiring board through guide rails on a housing and including warpage preventing unit that protects the printed wiring board against warpage and a fall preventing unit that prevents the board from falling (summary, FIG. 1, etc.). Japanese Laid-Open Patent Publication No. 57-07998 discloses linking a printed board and a heavy-part loading board with a distance and placing into a printed-board housing unit the printed board and the heavy-part loading board being supported with guiding grooves corresponding to the printed board and the heavy-part loading board (detailed description of the invention, FIG. 2, etc.).
It is desired that a printed board unit loaded with heavy parts are prevented from tilting or falling due to the displacement of the gravity center to achieve stable insertion into a housing. However, if rails are respectively provided on the left and right lower sides of the unit to prevent falling (Japanese Laid-Open Patent Publication No. 57-07998), two guide rails corresponding to the two rails are necessary and, although a fall preventing unit may be provided (Japanese Laid-Open Patent Publication No. 09-08480), such a structure increases the number of parts, resulting in cost increase.
Although flowing of cooling air is essential for cooling heat generating parts loaded in a printed board unit, the number of disposed rails increases in proportion to the number of loaded printed board units and, if a guide rail is disposed for each of the rails, an area occupied by the guide rails reduces an area for sucking the cooling air and causes the reduction of the cooling efficiency of an apparatus or the heat generating parts.
With regard to a server apparatus using such rails and guide rails, a server apparatus 2 depicted in FIG. 1 has four printed board units 61, 62, 63 and 64 disposed in a housing 4, respectively, and a cooling fan device 12 combining a plurality of fan units 10 is disposed on the upper side of the housing 4 for cooling heat generating parts 8, etc.
As depicted in FIG. 2, two guide rails 14 and 16 corresponding to each of the printed board units 61 to 64 are arranged on the inner bottom portion of the housing 4, respectively. As depicted in FIGS. 3 and 4, rails 20 and 22 to be supported by the guide rails 14 and 16 are attached to the bottom edges of a frame 18 of each of the printed board units 61 to 64.
When L1 denotes a unit width of each of the printed board units 61 to 64 and L2 denotes an inner distance between the guide rails 14 and 16, the inner distance L2 is set smaller than the unit width L1. Each of the printed board units 61 to 64 has a cavity form with the bottom side thereof and the top side opened to ambient air and, when the cooling fan device 12 is activated, cooling air 24 (FIG. 5) passes through the printed board units 61 to 64 from the bottom side and flows into the cooling fan device 12. In this case, an area for sucking the cooling air 24 is formed in accordance with the inner distance L2 of the guide rails 14 and 16 rather than the unit width L1. That is, the flow rate of the cooling air 24 is reduced by a difference between the unit width L1 and the inner distance L2 (L1−L2=ΔL).
In an enlarged view of the guide rails 14 and 16 and adjacent part thereto, as depicted in FIG. 5, a main flow passage 26 of the cooling air 24 flowing for cooling the heat generating part 8 is formed in each of the printed board units 61 and 62. When L3 denotes a distance between the adjacent printed board units 61 and 62, this distance L3 forms a leakage passage 28 of the cooling air 24 and the cooling air 24 flowing through the leakage passage 28 makes no contribution to the cooling of the heat generating part 8 and is wasted. When n denotes the number of disposed printed board units, the number of distances is (n−1) and a total distance Lm of the leakage passages 28 formed in the housing 4 is as follows:Lm=(n−1)×L3  (1)
In this case, since n=4, the total distance is Lm=3×L3.
When t denotes a thickness of a metal plate forming the guide rail 16, since the distance L3 includes the thickness t of the guide rail 16 side, the distance for the leakage passage 28 is reduced to (L3−t) in this case. However, the thickness t is small and does not lead to the reduction of the cooling air 24 flowing through the leakage passage 28.
The leakage passage 28 increases in proportion to the number of the disposed printed board units 61 to 64 in the housing 4 and, for example, in the case of the four printed board units 61 to 64 as depicted in FIG. 6, the number of the leakage passages 28 is three. The cooling air 24 flowing through these leakage passages 28 is exhausted to the outside through a duct 30 disposed on the upper side of the housing 4 along with the cooling air 24 flowing through the main flow passages 26.
As depicted in FIGS. 7 and 8, the adjacent guide rails 14 and 16 are disposed with a distance L4 provided therebetween. The distance L4 is set to a width allowing the above distance L3 to be ensured. Guides 32 are made up within the distance L4 by cutting and raising entries of the guide rails 14 and 16 to make protrusion in the width directions. Useless space exists between the adjacent printed board units 61 and 62, between the printed board units 62 and 63, and between the printed board units 63 and 64 as above and causes the disposition areas of the printed board units 61 to 64 and the volumes of the printed board units 61 to 64 to be narrowed.
Such problems are not suggested or disclosed and a means for solving the problems is not disclosed in Japanese Laid-Open Patent Publication No. 09-08480 and Japanese Laid-Open Patent Publication No. 57-07998.